1. Field of the Invention
This invention relates to a method for controlling the shape of material in rolling processes, and more particularly to a method for controlling the shape of a cold-rolled material.
2. Discussion of Background
For the control of the shape of rolled material which is obtained by a cold rolling operation, it has been the conventional practice to employ the thermal crown control in addition to the work roll bending control which control the roll camber by varying the bending load of the work roll.
Shown in FIG. 1 is a typical thermal crown control method, in which a plurality of coolant spout nozzles 2 are provided at intervals in the axial direction of a barrel shaft of a work roll 1 for spurting a roll coolant therefrom, and the shape of the rolled material is detected by a shape detector (not shown) which produces shape parameters P as its output signal. The shape parameters P are led to a coolant supply control unit 20 thereby to calculate a local deviation .epsilon.(j) of the shape parameter P at a position j in the axial direction of the barrel shaft from a target shape parameter M, supplying a valve opening control signal proportional to the local deviation .epsilon.(j) to a flow control valve 3 for a coolant spout nozzle 2 which is located at the position j in the axial direction of the barrel shaft. Indicated at 4 is a roll coolant circulating tank, at 5 a feed pump, and at 6 is a main piping.
The above-described conventional method, however, has a problem in that the cooling capacity of the roll coolant becomes insufficient even at a maximum flow rate in some cases because the temperature of the roll coolant is at a constant level. Of course, it is possible to provide a roll coolant of a lower temperature (a cold coolant) in addition to the ordinary roll coolant (a hot coolant), and to switch to the cold coolant when the cooling capacity beomes deficient. The cooling capacity can be increased by this method, but there arises another problem that the sudden change of the cooling capacity makes the control of the thermal crown discontinuous. Further, in a case where the rolled strip contains a sheet crown, the accuracy of the shape control is impaired by variations in the contact angle of the rolled strip with the shape detector or sensor roller in the width wise direction of the strip, which cause differences in detected axial load between the center and end portions of the strip.